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onsdag 21 maj 2014

Tao on Clay Navier-Stokes and Turbulence?

Terence Tao is working on the Clay Navier-Stokes Prize Problem and in a recent post considers  Kolmogorov's power law for turbulence. A heuristic derivation goes as follows: The smallest spatial scale \epsilon of a fluctuation u of turbulent incompressible flow of small viscosity \nu >0 is determined by a local Reynolds number condition
  • \frac{u\epsilon}{\nu}\sim 1.
Assuming the smallest scale carries a substantial part of the total dissipation gives 
  • \nu(\frac{u}{\epsilon})^2\sim 1.
Combination gives 
  • u\sim \nu^{\frac{1}{4}}
  • \epsilon\sim\nu^{\frac{3}{4}} 
suggesting that the turbulent solution is Lipschitz continuous with exponent \frac{1}{3}

My question to Tao posed as a post comment is if according to the Clay problem formulation, such a Lip^\frac{1}{3} turbulent solution with smallest scale \nu^\frac{3}{4} is to be viewed as a smooth solution for any small \nu >0?

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